Has anyone ever heard of Losing Christina, by Caroline B. Cooney? It's a very good series.

It's about a Maine girl, who has lived on Burning Fog Island, off the coast of the mainland. The children of Burning Fog go through elementary school on the island, and come to the mainland for middle school. Christina, Anya, Micheal, and Benj all go to board with the principal's family. Who better? But something evil is happening at the Shevvington's house.
In Fog, Anya slowly begins to loose her mind, and Christina knows the Shevvingtons are behind it.
In Snow, the Shevvingtons bring Dolly to live with them when they realize Christina is too strong for them to control. Sweet, sweet Dolly seems to be lost in a snowstorm, but Christina knows she is really lost in the house, and that is much much worse.
In Fire, the final book in the series, Christina finally finds the evidence she needs to expose the Shevvingtons. Can she do it before everything goes up in flames?

Sorry for the huge summary xD
But, it is a VERY good series.

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